A telephone device such as a private branch exchange to be connected with a public line network is generally installed to accommodate a plurality of analog telephones to be used as extension telephones in this telephone device. Furthermore, this telephone system is controlled by the telephone device so as to realize an outside line call via a public telephone network and an extension line call between extension telephones.
Described hereinafter is an operation for a case in which an incoming call is received by this telephone system on an outside line.
When an outside line incoming call occurs, the telephone device outputs a call signal to each analog telephone accommodated therein. Each analog telephone, having received the call signal, enters an incoming call ringing state.
For example, each analog telephone, having entered the incoming call ringing state, rings a ringtone and flashes an LED (light emitting diode) indicating the occurrence of the incoming call to notify a user of each analog telephone of the incoming call.
Each user, having detected the incoming call based on this notification, takes a receiver of the analog telephone off hook. Accordingly, the telephone device connects the analog telephone, which is in the hooked-off state, and a telephone which is the source of the incoming call thereby realizing a call enabled state. That is, the analog telephone is taken off hook (“hooked off”) to respond to an outside line incoming call.
Thus, when an analog telephone, accommodated in the telephone device, is taken off hook when an incoming call cause the analog telephone to ring in response to the call signal, the analog telephone makes an immediate response. Therefore, the analog telephone cannot perform a calling operation during a state when it is ringing. In this case, to perform a calling operation, a user has needed to wait for another user to respond to the incoming call by using another analog telephone or wait for the call source to stop calling.
Therefore, for example, it is inconvenient for users who make frequent calls and have little occasion to respond to an outside line incoming call for business, to use such a telephone device.
In view of this point, a plurality of analog telephones accommodated in a private branch exchange need to be installed by being grouped as i) analog telephones which ring in response to an incoming call, and ii) analog telephones which are not allowed to ring in response to an incoming call, in order to allow the above described users who make frequent calls to use the analog telephones to make out going calls.
Alternatively, it has been necessary to make settings in advance similar to those in a technique disclosed in Patent Literature 1. More specifically, it has been necessary to make settings of linking in advance a call number of an outside line incoming call and an extension line number of a person who deals with this call number and causing only a telephone of the extension line number of the person who deals with the call number of the outside line incoming call to ring when there is actually an outside line incoming call (see Patent Literature 1).